Treatment of hydrocarbon gases by hydration



May 8, 1945- A. J. L. HUTCHINSON ETAL 2,375,559

TREATMENT OF HYBROCARBON GASES BY HYDRATION Filed 001;. 20, 1941 /Vrkprr 6722121905 Ove/arrivino /40 Srama- 757 (nella Enke/:1e M@ Patented May 8, 1945 CFFICE TREAMT'FHYDROCARBON GASES v BY nYnaA'rroN Arthur J. L. Hutchinson and Ira C. Bechtold, Los

Angeles, Calif., assignors to The Fluor Corporation, Ltd., Los Angeles, Calif., a corporation of California Application October 20, 1941, Serial No. 415,686

16 Claims.

vThis invention has to do with improved proc; esses applicable generally to the treatment of various gases or mixtures of gases partially or entirely capable of conversion into solid hydrates, i. e., water-addition products. 'Iypical ofsuch gases are natural gas, oil refinery (straight-run or cracked) gases, and various other industrial gases, all of which may be characterized as hydrocarbon gases but which may contain nonhydrocarbon constituents capable of hydration, such as carbon dioxide, hydrogen sulphide, and sulphur dioxide. It will be understood that the invention is principally concerned with improved systems for forming the hydrates and separating the latter from non-hydrated uid constituents of the gas, and it is contemplated that after their formation and separation, the solid hydrates may be used or further treated to serve the requirements of any particular purpose.

Generally speaking, the convertible constituents of the gases are transformed into their solid hydrates by maintaining the gas in intimate admixture with water under temperature and pressure conditions at which the hydrates will form. These conditions may of course vary within rather wide limits, depending upon the particular constituent or constituents of the gas to be hydrated. As an example, hydrates of the hydrocarbon series methane, ethane, propane, and butane (including isomers) may be converted to their solid hydrates at temperatures from about 35 F. to 40 F. and under pressures ranging, say, from 25 to 650 lbs. per sq. in. gauge. -4It is understood, of course, that particular gases or mixtures thereof may be convertible at selected combinations of temperature and pressure within the above ranges. Hydrates of non-hydrocarbon constituents of the gas, e. g., carbon dioxide, hydrogen sulphide, and sulphur dioxide, may form along with the hydrocarbon hydrates although the temperatures and pressures actually required for hydration of the non-hydrocarbon compounds may be considerably lower, or higher, than those required for conversion of the hydrocarbons.

Formation of the hydrates may be employed for such typical purposes as storage of the hydrated compounds, as later explained; or to secure separation of relatively low boiling hydratable constituents of the gas from high boiling fractions incapable of hydration, as in natural gasoline refining explained in our copending application Serial No. 416,774, entitled Treatment of gaseous hydrocarbons, and filed October 27, 1941; or for purposes of fractionation and pres- Arthur J. L. Hutchinson, Ser. No. 392,186, led May 6, 1941, on Fractionation of hydrate-forming hydrocarbons; or to obtain a molecular concentration of a constituent of the gas to be treated with a reagent, as explained in our copending application entitled Treatment of gases, Serial No. 416,774, flled October 2'7, 1941.

It has been determined that the efficiency and completeness of hydrate formation are enhanced by maintaining the gas and water mixture in a state of active or turbulent agitation, effects of which are to increase surface contacts between the gas and water, maintain the Water particles in a state of ne division, promote formation of the hydrate crystals, and facilitate dispersion or entrainment and movement of the hydrates in the iluid stream. In accordance with the invention, we have provided an :improved method for satisfying these conditions, whereby the gas and water are introduced into an elongated passage of relatively small cross-sectional area at a rate such that an intimate mixture of the gas and water lls the passage and assumes turbulent flow therethrough. By proper control of the mixing temperature, with or without precooling the gas and water prior to their introduction to the mixing passage, and by maintaining the mixture stream under a pressure required for conversion of al1 constituents of the gas desired to be hydrated, complete hydration of such constituents occurs during the course of flow through the mixing passage. The turbulence of iiow effectively entrains all the hydrate crystals at the instant of their formation, permitting continuous and complete removal of solid, as well as fluid, phases of the stream into a zone of separation. As will be apparent, one outstanding advantage of the system is its complete simplicity from standpoints both of equipment and method of operation.

The invention contemplates various additional expedients tending to secure such advantages as maximum and controllable degree of dispersion and particle size of the water admixed with the gas, and the removal from the mixture stream of heat of hydrate formation which otherwise might inhibit hydration or otherwise adversely affect the mixing operation. It is found that maintenance of the water in a state of fine division desirable for the formation of small-size hydrate crystals, may be aided by the presence in sure generation described in the application of the water-gas mixture of a non-aqueous carrier liquid, preferably a petroleum fraction such as kerosene distillate, or perhaps gas oil corresponding somewhat more closely to the specific gravity of the hydrate. The carrier liquid serves not only as a dispersing medium for the water, but also, as the term implies, as a carrier medium for transferring the hydrates from their locus of formation to any other zone for storage or further treatment according to the ultimate purpose of the process.

As a further aid i`n promoting'ne particle size dispersion of the water and resultant formation of small hydrate crystals, we propose to use an emulsifying agent which may be introduced in any suitable manner to the water-gas mixture. Ordinarily it will be preferred to mix the emulsifying agent with the water or carrier liquid, or both, prior to their injection into the gas stream Further features are contemplated', such as cooling the mixture in the elongated mixing passage, either indirectly by external application of a cooling medium, or internally by injecting a cooling fluid directly into the mixture. For the latter purpose, we may introduce to the mixture streamat one or more locations a cold nonaqueous carrier liquid, all as will hereinafter appear. It is also contemplated that the mixture stream may be cooled, or maintained within proper temperature limits, by the introduction of ice particles which have capacity for compensating, by their heat of fusion, for heat of formation of the hydrates, in order to keep the temperature of the stream desirably low. Any of these methods of cooling the Water-gas mixture may be employed to maintain the stream at temperatures permitting complete formation of the hydrates. I

The details of the process will be understood to better advantage from the following description of certain typical hydrate-forming systems embodying the invention, as shown in the accompanying drawing, in which:

Fig. 1 illustrates diagrammatically and in flow rate sumcient to flll completely the passage and pass at fairly high velocity in a state of turbulent l ow. Incipient 'hydrate formation occurs imme-y diately upon mixing of the gas and water, and continues toward complete conversion of the gas constituents capable of hydration under the existing temperature and pressure conditions, along the course of flow of the mixture in line I3. Formation of the hydrates develops heat, i. e., heat of hydrate formation, .which it may be desirable 4 to remove from the mixture stream in order vand then to dispose further of the separated sheet form one method involving indirect cooling in the temperature range required for hydrate. formation under the existing pressure. The gas.

stream is forced by compressor I2 through an elongated mixing passage comprising a pipe I3 which may beof any desired length, depending upon time factors and the necessary turbulent flow of the water and gas mixture during the hydrate formation stage. Ordinarily the capacity of the system will determine the diameter of the mixing pipe I3, although its cross-sectional area will in any event be small as compared with the length of the passage. The water may be introduced through line II to a suitable container I4, wherein the water may be mixed (and, if desired, cooled by coil K) with carrier liquid introduced through line I5 or recirculated through line I6, where it is desired to use a carrier liquid and to introduce same at the initial stage of water-gas mixing. When an emulsifying agent is to be used, the agent also may be introduced with the water or into the container I 4, as through line I1.

The water `and any added carrier liquid or emulsifying agent are injected by pump I 8 through line I9 into the gas stream in the mixing passage I3, wherein the combined fluids flow at a phases according to particular purposes to be served. Merely as illustrative, we have shown the hydrates to be delivered for storage in one or more tanls or containers 24, 25, any desired number of which may be filled with the hydrates successively or alternately. As an example of the latter type of operation, the mixing passage stream may first be discharged through line 26 into storage vessel 24, wherein the solid hydrates settle and accumulate as a body supported on an apertured or liquid-permeable oor 21. Gaseous or uncondensed constituents of the mixture may be withdrawn through valved line 28, and liquid constituents separated from the solid hydrates in any suitable manner, as by withdrawing the lower specific gravity carrier liquid through line 29 from the storage zone at a high elevation and taking off any residual water and emulsifying agent from the bottom of the vessel through line 30. The separated carrier liquid may be recirculated through line I6 to container I4, and the water and emulsifying agent recirculated through lines 30 and 3I to tank I4. Suitable equipment, diagrammatically indicated at 32, may be employed for separating spent emulsifying agent from the Water, should it be found desirable to do so, and for returning the water through line 33 to storage I4.

When vessel 24 is filled with hydrates, valves 34, 35, and 36 may be closed and the hydrate body cooled or refrigerated by suitable means (not,y

shown) to maintain the hydrates in stabilized condition for storage. By closing valve 31 and opening valve 38, the flow from the mixing passage I3 may be diverted into storage vessel 25 and a second body of hydrates accumulated therein, as explained with reference to storage vessel 24. Gases and uncondensed vapors are withdrawn through line 39 and carrier liquid and residual water recirculated, respectively, vthrough lines 4I) and 4I. At such time as it is desired to utilize 'the gas stored in hydrated form in the vessels 24 and 25, the hydrates may be decomposed, as by heating, and the liberated gas discharged to line 42 through outlets 43 and 44. It may be mentioned that, if desired, while the vessels 24 and 25 are being filled with hydrates, all or part of the uncondensed gases and vapors may be recirculated to the mixing passage I3 through line 44| from the outlets 43, 44 and line 42, by

proper manipulation of the various valves illustrated.

Another purpose may be served by the gas recycle connection 44| with the mixing passage I3, in that this arrangement permits recycling gas liberated by limited decomposition of the stored-hydrates to maintain the hydrate beds at low stabilizing temperature. Depending upon the thermal efficiency of the vessels 24 and 25, more or less atmospheric heat will be transferred to the hydrates in storage, resulting of course in an increase in the hydrate vapor pressure and a tendency for some of the hydrates to decompose. By venting off relatively small amounts of gas through line 43 or line 44 to the gas recycle line 44|, a small percentage of the hydrates may be decomposed so that their heat of decomposition. supplied from the hydrate masses, will maintain their temperatures desirably low.

Provision may be made whereby a portion or all of the heat required to decompose the hydrates in vessels 24 and 25 may be supplied by the mixing passage streaml, thus utilizing the decomposition of previously formed hydrates as a means of removing heat of formation of hydrates subsequently forming in the mixing passage. Assuming the mixture in line I3 to be discharged into vessel 25 and that it is desirable simultaneously to decompose the hydrates in vessel 24, by closing valve 41 and opening valve 48 the mixing passage stream may be diverted through line I3a into heat exchanger 48| to supply heat to the hydrates being dissociated. The mixing Dassage stream then flows from the heat exchanger 48| into line I3, valve 48 being opened and valve 50 closed. When the hydrates are to be decomposed in vessel 25, the mixing passage flow occurs through line |3b, valves 48 and 50 vbeing closed, into heat exchanger 52 and then through line 53 into line I3 leading to the cooler 22.

Instead of serving to transfer heat from the gas-water mixture in stream I3 to decompose the stored or accumulated hydrates, heat exchangers 48| and 52 may similarly be used to cool the mixing passage stream by heat transference to ice bodies retained in the storage vessel after release of ther gas. By liberating gas from the storage vessels without heating the hydrates, as by merely opening the valves in the outlet lines 28 and39 to reduce .the pressure in the storage vessels, the hydrates will decompose by virtue of the pressure reduction alone and heat of fusion or decomposition will be supplied from the residual water. The

latter thus may be caused to freeze and remain as ice bodies in the storage vessels. By diverting the mixing passage stream through the heat exchangers 48| and 52 after formation of the icewbodies, considerable cooling of the mixing passage stream may be effected by the transferenelof heat to melt the ice.

The system shown in Fig. 2 is generally similarto the flow diagram of Fig. 1, but differs principally with respect to the conditions under which the water and carrier liquid are admixed with thegas in the elongated mixing passage. As before, the gas introduced to the mixing passage 3 is mixed with water, with or without carrier liquid and emulsifying agent, taken from storage |4 through `line I9. Under certain conditions it may be desirableV to contact the gas with water introduced at successive locations or stages in the mixing passage, and for this purpose, line I9 is shown to connect with a water supply manifold 54 from which individual streams of water in controllable amounts may be introduced to any suitably spaced points along the mixing passage, through valved branches 54a.

Instead of removing the heat of hydrate formation by indirect cooling of the mixing passage stream as in Fig. 1, the system of Fig. Zcontemplates direct cooling ofthe mixture by introducing a cooling medium into the mixing passage. As previously indicated, it is'contemplated that a portion or all of the water to be mixed with the gas may be introduced to the mixing passage in the form of ice particles or crystals. Tb illustrate one method adapted to serve the purpose, Fig. 2 shows a cooler at 80 through which a portion or all of the water-carrier liquid mixture may be forced by pump 8| to cool the mixture to a temperature at which the dispersed water particles will be frozen into ice crystals. The latter are returned in the carrier liquid stream through line 82 to be introduced at one or more locations 54a into the mixing passage stream. By this method the injected stream is given considerable cooling capacity either to lower the temperature of the mixing passage stream or to compensate for the heat of hydrate formation, by virtue of the heat of fusion of the ice particles.

We `have also referred to the possibility of injecting into the mixing passage a cooling iluid independent of the initially admixed water and gas` streams. This cooling fluid desirably may consist of the non-aqueous carrier liquid derived from a storage zone or from subsequent separation of the stream discharged from the :mixing passage, as will presently appear. It is also contemplated` that individual streams of the cooling fluid may be introduced to the mixing passage at successive locations, thus causing the water and gas mixture to be cooled in stages, and where the cooling iiuid consists of carrier liquid, to have stage dilution by the carrier liquid to aid in the transference of the progressively forming hydrates. As illustrative, carrier liquid that may have been cooled to a temperature approaching, or even below the freezing temperature of water, is introduced through line to a manifold 56 from which the liquid is discharged into spaced locations along the mixing passage through valve branches 56|, 51, and 58.

From passage I3 the `hydrate and carrier liquid mixture is discharged into one or the other `of storage vessels 59 and 60, from which gases and uncondensed vapors are vented through the outlets 8|. The hydrates are collected in the storage vessels and the carrier liquid, together with any residual water and emulsifying agent. is withdrawn through the bottom outlets 6". or 63 to a separator 64, within which the water and emulsifying agent gravitate to the bottom. The water is -withdrawn through line 65 for treatment at 66 to separate the emulsifying agent which is withdrawn through line 61, permitting recirculation of the water to the storage vessel I4 through line 68. The carrier oil is withdrawn from the separator B4 through line 69, and is forced by pump 10 through a cooler Il from which the cooled carrier passes to line 55. Any

recirculated carrier liquid in excess of the quan tity to be introduced to the mixing passage. may be recirculated to vessel I4 through line 12.

We have referred to the use of emulsifying agents to aid in promoting fine particle dispersion of the water admixed with the gas to be hydrated. Any suitable emulsifying agents, of which many are known, may be used. Typical agents are the commonly used organicsalts and fatty acid soaps which can eiectively emulsify the water and carrier liquid. We may prefer, however, to particularly form the emulsion to throw the water into the disperse phase, so that ilne particles or droplets of the water are enveloped in a continuous phase of the carrier oil. For this purpose, the emulsifying agent may be particularly selected to form a water-in-oil form of emulsion, from such known-agents as the fatty acid soap of ethylene diamine, marketed by National Oil Products under the trade name Nopco-DPM.

We claim:

1. The method of treating a normally gaseous hydrate-forming fluid that includes passing a stream of said fluid together with water-containing liquid through an elongated passage of relatively small cross-sectional area at a rate such that said stream fills said passage and assumes turbulent ow therein, the ratio of said liquid to said hydrate-forming fluid being such that the liquid forms a continuous phase throughout lsaid passage and said fluid forms a dispersed phase therein, maintaining said stream at temperature and pressure conditions causing said hydrate-forming fluid to be converted to solid hydrate particles which are entrained by said stream, and discharging the stream from said passage and separating the hydrates from said discharged stream.

2. The method of treating a normally gaseous hydrate-forming fluid that includes passing a stream of said fluid together with a water-containing non-aqueous carrier liquid through an elongated passage of relatively small cross-sectional area at a rate such that said stream fills said passage and assumes turbulent flow therein, the ratio ofA said liquid to said hydrate-forming fluid being such that the liquid forms a continuous phase `throughout said passage and said fluid forms a dispersed phase therein, maintaining said stream at temperature and pressurel conditions causing said hydrate-forming fluid to be converted to solid hydrate particles which are entrained by said carrier liquid, and discharging the stream from said passage and separating the hydrates from said discharged stream.'

3. The method of treating a normally gaseous hydrate-forming fluid that includes passing a stream of said fluid together with a water-containing petroleum fraction carrier liquid through an elongated passage of relatively small crosssectional area at a rate such that the stream fills said passage and assumes turbulent flow therein, the ratioof said liquid to said hydrateforming fluid being such that the liquid forms a continuous phase throughout said passage and said fluid forms a dispersed phase therein, maintaining said stream at temperature and pressure conditions causing said hydrate-forming fluid to be converted to solid hydrate particles which are entrained by said stream, and discharging the stream from said passage and separating the hydrates from said discharged stream.

4. The method of treating a normally gaseous hydrate-forming fluid that includes passing a stream of said fluid together with water emulsified with a Water-immiscible carrier liquid through an elongatedpassage of relatively small cross-sectional area at a rate such that the stream lls said passage and assumes turbulent flow therein, the ratio of said liquid to said hydrate-forming fluid being such that the liquid forms a continuous phase throughout said passage and said fluid forms a dispersed phase therein, maintaining said stream attemperature and pressure conditions causing said hydrate-forming uid to be converted to solid hydrate particles which are entrained by said stream, and discharging the stream from said passage and separating the hydrates from said discharged stream.

5. The method of treating a normally gaseous hydrate-forming fluid that 'includes passing a stream of said fluid together with water-containing liquid through an elongated passage of relatively small cross-sectional area at a rate such that the stream fills said passage and `assumes turbulent flow therein, the ratio of said liquid to said hydrate-forming fluid being such that the liquid forms a continuous phase throughout said passage and said fluid forms a dispersed phase therein, maintaining said stream at temperature and pressure conditions causing said hydrateforming fluid to be converted to solid hydrate particles which are entrained by said stream, cooling said stream, and discharging the stream from said passage and separating the hydrates from said discharged stream. l

6. The method of treating a normally gaseous hydrate-forming fluid that includes passing a stream of said iluidtogether with water-containing liquid through an elongated passage of relatively small cross-sectional area at a rate such that the stream fills said'passage and assumes turbulent flow therein, the ratio of said liquid to said hydrate-forming fluid being such that the liquid forms a continuous phase throughout said passage and said uid forms a dispersed phase therein, maintaining said stream at temperature and pressure conditions causing said hydrateforming fluid to be converted to 'solid hydrate particles which are entrained by said stream,

cooling said stream by introducing a cooling fluid thereto, andv discharging the stream from said passage and separating the hydrates from said discharged stream. f

' 7. The method of treating a normally gaseous hydrate-forming fiuid that includes passing a stream of said fluid together with water-containing liquid through an elongated passage of relatively small cross-sectional area at a rate suchA that the stream fills said passage and assumes turbulent flow therein, the ratio of said liquid to said hydrate-forming fluid being such that the liquid forms a continuous phase throughout said passage and said fluid forms a. dispersed phase therein, maintaining said stream at temperature and pressure conditions causing said hydrate-forming fluid'to be converted to solid hydrate particles-which are entrained by said stream, introducing to said stream a hydrate carrier iluid, and discharging the stream from said passage and separating the hydrates from said discharged stream.

8. 'I'he method of treating normally gaseous hydrate-forming fluid that includes passing a stream of said fluid together with water-containing liquid through an elongated passage of relatively small cross-sectional area at a rate such that the stream lls said passage and assumes turbulent flow therein, the ratio of said liquid to said hydrate-forming fluid being such -that the liquid forms a continuous phase throughout said passage and said fluid forms a dispersed phase therein, maintaining said stream at temperature and pressure conditions causing said hydrateforming fluid to be converted to solid hydrate particles which are entrained by said stream, introducing to successive locations in said stream a cool water-immisclble hydrate carrier liquid, and discharging the stream from saidv passage and separating the hydrates from said discharged stream.

9. The method of treating a normally gaseous hydrate-forming uid that includes passing a stream of said fluid together with water-containing liquid through an elongated passage of relatively small cross-sectional area at a rate such that the stream lls said passage and assumes turbulent flow therein, the ratio of said liquid to said hydrate-forming iluid being sucn that the liquid forms a continuous phase throughout said passage and said fluid forms a dispersed phase therein, maintaining said stream at temperature and pressure conditions causing said hydrateforming uid to be converted to solid hydrate particles which vare entrained by said stream, injecting into successive locations in said stream a hydrate carrier mineral oil cooled to a temperature below the freezing temperature of water, and discharging the stream from said passage and separating the hydrates from said i discharged stream. .-1

l0. The method of treating a normally gaseous hydrate-forming iluid that includes passing a stream of said fluid together with water-containing liquid through an elongated passage of relatively small cross-sectional area at a rate such that the stream nils said passage and assumes turbulent ow therein, the ratio of said liduid to said hydrate-forming iluid being such that the liquid forms a continuous phase throughout said passage and said fluid forms a dispersed phase therein, introducing water to the stream at succes sive locations therein, maintaining said stream at temperature and pressure conditions causing `said hydrate-forming fluid to be converted to solid hydrate particles which are entrained by said stream, and discharging the stream from said passage and separating the hydrates from said discharged stream.

. phase therein, maintaining said stream at temperature and pressure conditions causing said hydrate-forming :duid to be converted to solid hydrate particles which are entrained by said stream, discharging the stream from said passage, separating the hydrates from said discharged stream, separating residual water from said discharged stream, and admixlng the separated water with the yfirst named stream.

12. 'Ihe method of treating a normally gaseous ,hydrate-forming iluld that includes passing a stream containing said iluid together with water anda non-aqueous carrier liquid through an elongated passage of relatively small cross-sectional area at a rate such that the stream fills said passage and assumes turbulent now therein, the ratio of said liquid to said hydrate-forming fluid being such that the liquid forms a continuous phase throughout said passage and said fluid forms a dispersed phase therein, maintaining said stream at temperature and pressure conditions causing said hydrate-forming fluid to be converted to solid hydrate particles which are entrained by said stream, discharging the stream from said passage, separating the hydrates from said discharged stream, separating the carrier liquid irom 'said discharged stream, and admixing the separated carrier liquid with the first named stream.` n

13. 'i'he method of treating a normally gaseous hydrate-iorming huid that includes passing a stream containing said fluid together With water and a non-aqueous carrier hquid through an elongated passage o1' relatively small cross-sectional area at a ra te such that the stream fills said passage and assumes turbulent iiow therein, the ratio oi' said liquid to said hydrate-forming :duid being such that the liquid forms a continuous phase throughout said passage and4 said nuid forms a dispersed phase therein, maintaining said stream at temperature and pressure conditions causing said hydrate-forming fluid to be converted to solid hydrate particles which are entrained` by said stream, discharging the stream from said passage, separating the hydrates from said discharged stream, separating the carrier liquid from said discharged stream, coo-ling the separated carrier liquid to aid in maintaining temperature conditions in the first named stream suitable for hydrate formation, and admixing the cooled carrier liquid with said first named` stream.

14. Themethod of treating a normally gaseous hydrate-formingr duid that includes subjecting said duid to conversion into solid hydrates by forming a mixture of the fluid with water and a carrier liquid, passing -a stream of said mixture in heat transferring relationship with previously formed hydrates to aid in decomposing the hydrates and to cool said stream, then subjecting the stream of said mixture to pressure and temperature conditions at which said hydrates will form, and separating the hydrates from the carrier liquid. i

l5. The method of treating a normally gaseous hydrate-forming fluid that includes continuously passing a stream of said duid into a conversion zone and therein converting the iluid 'to solid hydrates under temperature and pressure conditions causing formation of the hydrates, compensating for heat of formation of the hydrates by introducing to said zone a liquid carrying particles of ice, and removing the hydrates from said zone in a stream of said liquid. l

16. The method of treating a normally gaseous l hydrate-forming fluid that includes continuously passing a stream of said uid into vla conversion" zone and therein converting the 4iluid to solid hydrates under temperature and pressure conditions causing formation of the hydrates, compensating for heat of formation of the hydrates by introducing to said zone a mineral oil carrying particles of ice, and removing the hydrates from said zone in a stream of said mineral oil..

ARTHUR J. L. HU'rcHrN-soN. mA c.BEcH'roLD. i 

